Overheating

The heat from the sun’s rays is a significant cause of overheating in buildings.

It causes discomfort for the people inside them and, as a result, energy use to remove the unwanted heat. Solar shading helps reduce and control solar gain, improving the wellbeing and productivity of occupants and reducing the need for artificial cooling measures.

The Problem

  • The power of the sun is infinitely variable. It is a dynamic force and glazing is typically static so cannot adequately cope with the variability of the sun’s irradiation
  • Typically, glazing in the UK is designed to retain winter heat with low-e coatings but these also prevent excess summer heat from escaping
  • Thermally inefficient glazing units have interior surface temperatures which differ from the temperature of the other surfaces and the mean air temperature. This results in uncomfortable internal conditions which energy-intensive mechanical air conditioning can’t help with

The Solution

Solar shading can help regulate solar gain in buildings by reflecting excess heat. This is particularly true of external shading or shading within ventilated facades.

But internal shading – the most popular type of shading in the UK – with reflective coatings can also help control excess solar irradiation.

Shading goes hand-in-hand with ventilation strategies, as warm air needs to be removed from buildings to help keep internal temperatures comfortable.

Linking solar shading to environmental systems or environmental controls ensures the shading position is optimised through automation.

The latest research

The Zero Carbon Hub’s report Overheating in Homes – The Big Picture (2015) says overheating is occurring in up to 20% of England’s housing stock with more expected to be affected in the future.

Professor Heiselberg, of Aalborg University in Denmark, states in his work on passive cooling that modern air-tight, well-insulated buildings have an increased need for cooling; not only in the summer but most of the year. He also explains that excessively high indoor temperatures are the most commonly reported problem in post-occupancy studies, even during the heating season.

Lord Krebs, of the Climate Change Commission, highlights a study headed by Professor Alan Short of Cambridge University.

It states that hospital wards vulnerable to overheating currently make up 90% of the total stock by floor space. The report goes on to say that one solution is external shading devices, as retro-fitting air conditioning would be uneconomic.

In offices, homes and hospitals, solar shading is identified as a key, passive solution to overheating.

Key measurement

G-value is the measurement of total solar energy transmittance through an object, such as glazing.

However, gtot is the more relevant measurement because it combines the total solar energy transmittance through the glazing and shading.

The Shard building in London is fully-glazed with a double-skinned façade containing automated blinds. Its architects have acknowledged it would not have been possible without solar shading.

With its interstitial blinds lowered, The Shard achieves a gtot of just 0.12 (88% heat rejection) – and this is a building clad entirely in glass.


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